Refining with hf and cbf5



July 13, 1954 A. P. LIEN ET AL REFINING WITH HF AND cbr; Filed sept. so, 1952 Patented July 13, 1954 UNITED STATE@ dTENT OFFICE REFINING WITH HF AND CbFs Arthur P. Lien, Highland, Ind., and David A. McCaulay, Chicago, lill., assignors to Standard Oil Company, Chicago, Ill., a corporation of Indiana Application September 30, 1952, Serial No. 312,279

17 Claims.

This invention relates to the rening of mixed hydrocarbon oils. More particularly, it relates to the refining of hydrocarbon oils which contain, in addition to other hydrocarbon compounds, aromatics, organic sulfur compounds, oxygenated compounds and nitrogen compounds. Further, the invention relates to the treatment ci isomeric dialkylbenzenes in order to effectuate the separation between isomers or groups of isomers thereof. The invention is of particular interest in the separation of the isomeric xylenes.

Naturally occurring hydrocarbon oils are mixtures of various classes of hydrocarbons and various organic compounds containing one or more of the elements sulfur, oxygen and nitrogen. For some uses many hydrocarbon oils contain an objectionable amount of aromatic hydrocarbons, e. g., diesel oils, kerosenes, domestic fuel oils and lubricating oils. For some uses hydrocarbon oils should not only be low in aromatics, but also low in organic sulfur compounds. In some cases such as coal tar distillate, the oil contains substantially only aromatics and some organic sulfur compounds, and it is desired to remove the sulfur compounds only. in the case of shale oil, it is desirable to remove not only sulfur compounds, but also nitrogen compounds and oxygen compounds. One of the better methods for reiining of a mixed hydrocarbon oil containing objectionable amounts of aromatic hydrocarbons and organic sulfur compounds is to treat with liquid hydrogen iiuoride containing boron trirluoride. The HF-BFg treating agent acts very much like a selective solvent. However, this process has the serious disadvantage of having tc operate at high pressures when temperatures above ambient are used because the BFS is a very volatile gas. Another method for improving the quality of heavy hydrocarbon oils such as lubricating oils is by treatment with liquid HF and silver iiuoride as disclosed in U. S. 2,531,723.

It is wel known that the isomeric dialkylbenrene-s cannot be resolved into high purity isomers by fractional distillation; particularly this is true when the mixture of isomers also contains close boiling non-aromatic hydrocarbons, e. g., a mixture of C8 aromatic hydrocarbons and nonaromatic hydrocarbons can be at best resolved into an orthoxylene concentrate containing about '70% o-xyiene and a lower boiling concentrate. in View of the commercial importance of the various xylene isomers, a considerable incentive exists for the recovery of high purity xylene isomers from mixtures thereof. To a lesser extent the high purity isomers of other 2 dialkylbenzenes such as diethylbenzene, di-npropylbenzene, etc. are of interest. Y, It is an object of this invention to refine mixed hydrocarbon oils by an extraction method. Another object is the removal of aromatic'hydrw carbons, organic sulfur compounds and phenolic compounds from hydrocarbon oils containing objectionable amounts of these materials. A5 further object is the rening of lubricating oil distille-tes to improve the viscosity index thereof.

Still another object of this invention is a process for the separation of individual dialkylbenzene isomers from a mixture of isomers oi' said dialkylbenzene, e. g., xylene isomers. An additional object is a process for the recovery of a metaxylene enriched fraction from mixtures oi m-xyiene with at least one other Xylene isomer. A particular object is the treatment oi a hydrocarbon fraction in the C3 aromatic hydrocarbon-boiling range for the separation .of the C8 aromatic hydrocarbons therefrom and the further treat-j ment of said Cs aromatic hydrocarbons to obtain high purity m-xylene, o-xylene and p-xylene fractions. Other objects oi the invention will be apparent in the detailed description thereof.

It has been discovered that several oi the objects of this invention can be attained by treating hydrocarbon oils which contain appreciable amounts of aromatic hydrocarbons, and/or organic sufur compounds. and/or phenolic com pounds, and/or nitrogen compounds by treating said hydrocarbon oils with columbium pentaiiuoride-CbFs--in the presence of a sufiicient amount of substantially anhydrous liquid HF to form a separate 1ELF-rich phase. c

It has further been discovered that a hydrocarbon oil whichcontains dialkylbenzenes and polyalkylbenzenes can be substantiaily coinpletely freed of said dialkylbenzenes and polyalkylbenzenes by treatment with an amount of substantially anhydrous liquid HF to form a separate HLP-rich phase and at least about i mol of CbFs per mol of said dialkylbenzenes and poly.- alkylbenzenes. Y

It has been discovered that by the treatment of a mixture or" at least two isomeric diailiylbenzenes with suiiicient liquid HF to form a separate BIF-rich phase and less than about l mol of CbFb per mol of said dialkylbenzenes, a separation can be eiected between said isomers. It has been found Athat the HF-rich (extract) phase will contain a mixture of said isomers wherein the molar ratio thereof is different from the ratio in the feed; and the raffinate phase Will contain a mixture of said isomers wherein 3 the molar ratio thereof is different from the ratio in the feed. The meta-isomer is preferentially extracted into the extract phase. When treating a mixture of ortho and para-isomers the ortho-isomer is preferentially extracted into the extract phase.

The feed to our mixed hydrocarbon oil refining process can be: various fractions obtained from the distillation of crude oil, e. g., naphthas, kerosenes, heater oil, lube oils, etc., or the crude oil itself, or reduced crudes. Another class of materials suitable as a feed may be oils derived from the treatment of the above materials, e. g., raiiinates and extracts from the solvent treatment of kerosenes or lube oils. Shale oil, and its various fractions, is a suitable feed to our process. The so-called light oil from the ccking lof coal is an exceptional feed to our process since the sulfur compounds in the benzene and' toluene fractions are extremely refractory to conventional desulfurization methods. The lieuid products from the hydrogenation of coal or the Fischer-Tropsch process are suitable feeds to our process. Liquid HF--CbF is a powerful catalyst for alkylation purposes. Appreciable amounts of oleins can be eliminated from olefin-containing feeds by treatment with liquid HF-CbFs the alkylate may or may not be extracted into the extract phase. In general, oils containing large amounts of oleiins are not a desirable feed to our process. 'In general, the most suitable feed stocks are petroleum distillates boilingin the heavier-than-gasoline range, i. e., above about 350 F. and below about 750 F., and particularly those distille-tes derived from high sulfur and high aromatic content crudes, such as, West Texas crude, Winkler crude, etc.

Columbium pentafluoride is a crystalline solid having a melting point of about 168 F. and a boiling point of about 444 F. The solid is appreciably soluble in substantially anhydrous liquid HF. It has been discovered -that the solubility of CbFs in substantially anhydrous liquid HF is greatly increased when a polyalkyl aromatic hydrocarbon, a polynuclear aromatic hydrocarbon, many types of organic sulfur compounds, or phenolic compound is brought into contact with CbFs, in the presence of substantially anhydrous liquid H-F. For example, a mixture of liquid HF and solid CbF5 is readily changed to a clear liquid when the mixture is contacted with a 'suicient mount of Xylene (no significant change in properties is obtainable by the treatment of a mixed hydrocarbon oil WithCbFs in the absence of sub- 'stantially anhydrous liquid HF) Columbium pentaiiuoride is readily decomposed by water. The process of this invention Vshould 'be carried out under vsubstantially anhydrous conditions. The liquid HF used in 'the process l should not contain more than about 1 or 2% of water, i. e., the liquid HF should be substantially anhydrous.

We have discovered that organic sulfur compounds and -some aromatic compounds not-amenable to removal by liquid l-IF treatment are removable from the raw oil by treating said oil with CbFs in the presence ofV sufiicient liquid HF to form a separate HF-rich phase. The l-lF-rich phase, hereafter called the extract phase, contains liquid HF, aromatics, organic sulfur compounds, phenolic compounds, some non-aromatics and 'CbFa i. e., if all of these organ-ic compounds are present in said oil. It is believed that the 'CbF5 in the extract phase exists in the form of a coordination compound or adduct with the aromatics and organic sulfur and phenolic ccmpounds. Benzene and toluene can exist in the extract phase in about the amount soluble in liquid HF alone, which amount is about 2-3 volume percent based on HF. By using a suiiicient amount of CbF5 and a sufficient amount of liquid HF, it is possible to produce a refined oil which contains substantially no compounds other than non-aromatics and benzene and/or toluene, if these aromatics are present in the raw oil.

Some improvement in quality of the oil can be obtained by using even a trace amount of CbF5 and further improvements can be obtained by increasing the amount of CbFs until substantially all the materials removable by the liquid `HF--Cblls treating agent have been removed. In general, the larger the amount of extractable materials present, the more CbFs needed in the treatment. The upper limit on CbFt usage is readily determined by the fact that when a solid CbF5 phase appears, no further improvement is obtainable. By the time that this third phase of solid CbFs appears, a sufficiently refined oil has usually been attained. Thus we can use between a trace amount of CbFs and an amount of CbFs that will not dissolve completely into the extract phase. Expressing the CbF5 usage in another Way, We can use from 0.1` Weight percent to about 25 Weight percent and, in some cases to about 100 weight percent, based on the raw oil. The amount of CbFs needed to obtain a particular degree of renement is readily determinablc by smell scale treatment of samples of the raw oil.

Sufficient liquid HF must be present in the ex traction zone to form a separate HF-rich phase, i. e., extract phase. The minimum amount of liquid HF needed` will vary somewhat with the type of oil being treated and the extrsctable materials content of the raw oil. The viscosity of the raw oil affects phase separation and, in general, the more viscous the raw oil, the more H-F needed to obtain good phase separation. The presence of extractable materials in the liquid HF increases the viscosity of the extract phase so that good phase separation may be diiicult when treating raw oils containing large amounts of extractable materials with small amounts of HF. When treating naphthas and light gas oils the minimum HF usage may be as low as 5 volume percent, based on the raw oil. When treating lube stocks such as distillate for the production `of S. A. E. 20 oil, as much as 20 volume percent of liquid HF may be needed to obtain good phase separation. We prefer to use more than the bare minimum amount of liquid HF. As much as volume percent liquid HF has been used without detrimental effect. However, little significant gain in refinement is obtained by using very large amounts of liquid PF. For most raw oils satisfactory'phase separation and a satisfactory degree of reiinement can be obtained by using from about l0 to about 500 volume percent of liquid HF. We prefer to use between about 30 and 300 volume percent.

Since viscosity does have an appreciable ciect on Athe clean-ness'of the phase separation, the viscosity of the raw oil may be reduced by adding an inert diluent thereto. The diluent should be relatively inert to the solvent action of the treating agent and also to the catalytic action of the treating agent. Additionally, lthe diluent should be readily separable by distillation from the refined oil, although in some cases it may be desirable to leave the diluent in the refined oil.

aces-,7e3

and CbF5 in an amount which is at least uni--` molar with respect to the Xylenes present in said mixture.

When the feed stock to our process consists of a lower dialkyl-benzene wherein the alkyl radical contains between 1 and 5 carbon atoms, such as xylene, in admixture with non-aromatic hydrocarbons and/or benzene or toluene, contacting of said feed stool: with a sucient amount of our liquid HF-CbFs treating agent results in a rafiinate phase and an extract phase. The extract phase consists of liquid HF, complex and some physically dissolved hydrocarbons. The degree of removal of the xylene from the feed'is dependent upon the amount of CbFs present in the treating agent. Substantially complete removal of the xylene can'be achievedby using at least about l mol of CbF5 per mol of xylene present in the feed. In some cases, particularly when the ratio of non-complexible hydrocarbon to xylene is quite high, more than 1 mol of CbF.

per mol of xylene will be necessary to achieve substantially complete removal of xylene. The' amount of CbFs should be limited to about that amount which will be completely complexed or brought into solution` in the extract phase. We have found that solid CbFs present in the extract phase has a marked catalytic effect on the aromatic hydrocarbons in the extract phase and undesirable side reactions, such as, isomerization, disproportionation and evencracking may occur; this eiect is especially-apparent when operating at higher temperatures. La general, while we may use from as little as 0.1 mol of CbF5 per mol of dialkylbenzene in the feed to as much as 3 mols, we prefer to use between about 0.3 and 1.5 mols of CbFs per. mol of dialkylbenzene in the feed.

When monoalkylbenzenes, such as, ethylbenzene, propylbensene. isopropylbenzene, butylbenzene, etc. are present in the feed'stocl the liquid HF-CbFs treating agent catalyzes the rapid dispropcrtionation of these compounds to dialk-yl` benzenes. The dialkylbenzenes form complexes with CbFs and pass into the extract phase. Therefore, when these monoalkylbenzenes are present in the feed stocx, it is necessary to use suihcient CbF5 to complex with the corresponding dialkylbenzene as well as with the other dialkylbenzenes present in the` feed stock itself. When ethylbenzene and/or propylbenzene are present in the feed stock, we prefer to use 0.5 incl of CbF5 per mol of said compound in addition to that used for the dialkylbenzenes-present in the feed.

The maximum degree of separation of a mixture of two isomeric xylenes is attainable by using about l mol of CbFs per mol of the more stable complex isomer present in the feed. While a high purity meta-xylene, e. g., in excess of about 95%, cannot be separated from a mixture of xylenes in a singe contacting stage, it is possible to achieve this result by using a multi-stage or countercurrent tower operation.

Suflicient liquid HF must be present to'participate in the formation of the complex and to'dissolve the complex. We preferto use an excess over this amount in order to insurev the formation of a separate extract phase. In general, when operating with mixed feeds containing xylene, the use of about 5 volume percent of liquid HF based on the total fee will be sufci-ent'to form a separate extract phase. As much as 500 volume percent of liquidHF or more may be used. In generalthe use oflarger amounts of Vliquid-HF i; decompose.

assists in phase separation and also, surprisingly enough, decreases the amount of non-aromatic hydrocarbons present in the extract phase. We prefer to use between about 100 and 300 volume percent of liquid HF, based on total mixed feed.

Temperature is an important factor in our aromatic separation process. When the contacting is carried out at temperatures in -excess of about 125 F., side reactions take place, such as isomerization of meta-xylene to the equilibrium mixture of the three isomers and disproportionattion of the xylenes to higher alkylbenzenes. When operating at temperaturesbelow about 30 F., longer contact times are necessary to achieve good separations and, at temperatures below about 0 F., the disproportionation of ethylbenzene, etc. is` slowed down markedly, which is disadvantageous when treating ethylbenzene-containing feeds. Although we can operate at higher ternperatures by using very short contact times and by quenching the reaction mixture at the end of the contacting, we prefer to operate below about 100 F. Under some conditions of temperature, CbF5 usage and long Contact time, ortho and/or lpara-xylene are isomerized to the nieta-xylene isomer. When it is desired to minimize this isomerization, not only should temperature be held at less than about 90 F., but also contact times should be short and the amount of CbFr, used should be such that a minimum amount of ortho and/or para-xylcne are present in the extract phase.

Contacting times are dependent upon the temperature at which the contacting is carried out Al and upon the degree of agitation in the contacting Zone. When using normal methods of agitation, contacting'time may vary from little as l minute to as much as 3 or more'hours. In general when operating at between about 30 and 90 F. and with a feed from which it is desired to remove substantialy all the xylene isomers contained therein, a suitable contacting time is between about 1 minute and 30 minutes.

We have found that the organic sulfur compounds normally present to some extent in virtually all hydrocarbon mixtures form complexes with CbF5 andrHF. In general these sulfur compound complexes are more stable than the diallylbenzene complexes and are more diflicult to However, heating the complex to temperatures on the order of 480 F. will drive off theHF and thus dissociate trie complex. The alkylphenols which are normally present in cracked stocks also complex with CbFt and HF. These complexes tend to'interfere with phase separationv and also introduce undesired impurities into'the extract oil. In onder to eliminate this interference, feed stocks containing such alkylphenols should be dephenolized by a suitable treatment, e. g., washing with 25% aqueous caustic solution. We prefer a feed stock that is substantially free of alkylphenols and which is low in total'sulfur content, i. e., on the order of about 0.02 weight percent of sulfur, such as can be obtained by extraction with HF alone.

In order to eliminate insofar as possible the loss of the-desired dialxylbenzenes to polyalkylbenzenes by alkylation with olens present in a mixedfeed stock. we prefer to operate on a feed stock that is low inolen content, e. less than about 3 or 4 Ourprocess maybe applied to a mixture of hydrocarbons comprising aromatics, parafns, naphthenes and olens (along with associated phenolic and sulfur compounds) which boil in ferred operating temperatures.

' 9 the approximate boiling range of the particular dialkylbenzenes to be recovered. We prefer to operate on a feed which is low in the interfering phenolic compounds, sulfur compounds and olens.

A particularly suitable feed for our dialkylbenzene separation process is the naphtha derived from the so-called hydroforming process, i. e., from the vapor phase treatment of a virgin naphtha at 850 to 10.50 F. in the presence of hydrogen over a catalyst such as molybdena on an alumina support or a platinum-containing catalyst. The hydroformate from such a process is low enough in sulfur to permit operation without further desulfurization and is sufhciently low in olefin that little degradation of the desired xylene content results during the separation step.

Any hydrocarbon cil w -ich contains appreciable amounts of lower dialkylbenzenes can be charged to our process either directly or after suitable pretreatment to lower the sulfur and alkylphenol content. These feed stocks may be derived from the distillation of petroleum, from the thermal or catalytic cracking of naphthas from petroleum, from the hydroforming or hydrosulfurizaticn of virgin or cracked naphthas, or they may be derived from the coliing of coal or from the drip oil produced in the production of carbureted water gas or producer gas. Other sources of feed to our process are the highly aromatic extracts obtained by treating petroleum oils with selective solvents, such as, phenol, furiural, SO2 and the like; usually these extracts will have to be desulfurized prior to treatment by our process. It should be understood that our process is applicable to the extraction of dialkylbenzenes and particularly the extraction of meta-dialkylbenzenes from isomeric dialkylbenzcnes, regardless of the method by which the feed was prepared.

The more common feed stocks for our process are a mixture of dialkylbenzenes, non-aromatic hydrocarbons, benzene, toluene and ethylbenzene. The non-complexible materials, i. e., non-aromatic hydrocarbons, benzene and toluene usually form from 50 to 5 volume percent of the total feed. (Monoalkylbenzenes other than toluene are not considered non-complexible materials because their disproportionation results in the formation of a complexible material, for example, diethylbenzene.) Where xylene concentrates are available from superfractionation equipment, a feed stool; containingr 70 or 80% of xylene and ethylbenzene may be available. We have found that phase separation and selectivity are improved when the feed stock does not exceed about 50 volume percent of complexible hydrocai-bons.

When operating on a substantially pure xylene and ethylbenzene mixture we prefer to add from about 50 to 200 volume percent of an inert hydrocarbon diluent. The diluent should be a vparaiinic and/or naphthenic hydrocarbon or a mixture of hydrocarbons that is ylow in materials that would interfere with phase separation and that will be readily separable by simple matic hydrocarbons. We prefer to use as diluents parafnic and naphthenic hydrocarbons of low boiling point since these materials are not isomerized or cracked by the liquid HF at the pre- Suitable hydrocarbons are butane, pentane, hexane, heptane, petroleum ether, etc. When operating at low temperatures such as 30 F. the diluents might be ihigher boiling paraiiinic or naphthenic hydrocarbons containing 10 or 11 carbon atoms. general when treating a mixed feed stock to remove substantially all the dialkylbenzenes, sucient non-complexible hydrocarbons will be present in the feed so that no additional diluent is needed. We prefer to operate with an amount of non-complexible hydrocarbons, i. e., present either as diluent or naturally; which amount is about equal in amount to the extractable hydrocarbons present.

The non-aromatic hydrocarbons extracted from the feed by the treating agent boil in about the same range as the aromatic hydrocarbons. Their presence decreases the purity of the aromatic hydrocarbons and they must be removed in order to obtain substantially pure aromatics as the final product. We have found that these non-aromatic hydrocarbons can be readily displaced from the extract phase by washing the extract phase with an inert diluent non-aromatic type hydrocarbon such as pentane, hexane or a 10- or ll-carbon atom paraffin. A single stage washing operation is usually suihcient to reduce the non-aromatic content of the extract phase to a point where substantially pure aromatics can be obtained by simple fractional distillation of the recovered aromatic hydrocarbons.

The raiiinate phase from our process will usually contain some dissolved liquid HF and also some entrained HF; small amounts of solid CbFs may also be entrained. The CbF5 can be recovered by filtration, by a coalescing operation or in some cases by distilling the raflinate oil. The liquid HF is readily removed from the raiinate phase lby distillation at temperatures of about F., at atmospheric pressure. In some cases the raihnate may contain minor amounts of valkyl uorides; these can be readily removed by percolation through bauxite.

The exact phase is readily decomposed by treatment with water, preferably cold water or ice; the upper layer of extract oil can be decanted from the lower aqueous layer. The extract oil contains the extracted materials, i. e., hydrocarbons and/or organic sulfur compounds. The lower aqueous layer consists or a mixture of hydrouoric acid and CbFe decomposition product. The extract oil can be freed of traces of HF by treatment with dilute caustic. This method is particularly suitable for laboratory operations.

We prefer to decompose the extract phase as follows: The extract phase is placed in a vessel, usually provided With a few fractionation trays, wherein the temperature of the extract phase is raised until the HF vaporizes and passes out of the vessel. The top temperature in the decomposing Vessel is held at about the boiling point of HF in order to prevent the removal of extract materials along with the HF. In the bottom of the decomposer after the removal of HF, there exists a slurry of extract materials and solid finely divided CbF5. This slurry is passed to a filter which retains the solid CbFs. The CbFs can be reused in the process. In the case of lower boiling extract materials, the extract materials may be distilled leaving behind the solid Cbll5. By operating under vacuum, the HF may be removed at low temperatures. We may operate at temperatures up toabout 400 F.; the lowest possible temperature is preferred because of the side-reactions resulting from the catalytic action of the treating agent. Where it is desired to avoid side-reactions in the extract phase, the decomposer may be operated under vacuum in order to remove a major part of the liquid HF aesarcs' 11 at temperatures below about 100 F.; and then the partially denuded extract phase is heated to from 200 to 400 F. to remove the remainder of the HF.

The results obtainable with our isomeric dialkylbenzene separation process are illustrated by the following example: In this test the contacting was carried out in a carbon steel reac tor equipped with a 1725 R. P. M. stirrer. rEhe CbF was prepared by the reaction of CbCls and liquid HF. A considerable excess of liquid HF over the theoretical amount and 0.4 mol of CbCl5 were agitated in the reactor at ambient temperature until the reaction was complete as indicated by a substantially constant pressure of about 235 p. s. i. g. The HC1 and excess HF were evacuated from the reactor leaving therein the CbFs product.

The feed to this test consisted of a synthetic blend of 60 volume percent n-heptane, 20 Volume percent m-xylene and volume percent of p-xylene; the feed blend contained 0.8 mol of xylene. Substantially anhydrous liquid HF equal to 160 volume percent, based on total feed, was introduced into the reactor and then the feed was introduced therein. The contents of the reactor' were agitated at about 68 F. for 60 minutes. The contents of the reactor were then permitted to settle for about l0 minutes before being withdrawn.

The lower extract phase was withdrawn into a vessel containing crushed ice; the hydrocarbons from the decomposed extract phase were decanted away from the aqueous layer and contacted with dilute aqueous caustic solution to remove traces of treating agent. The rail-mate and the extract were analyzed by combination of infrared analysis, specific gravity and refractive index methods.

The raiiinate was found to contain 25.3 volume percent of xylenes and the extract was found to contain 97% of xylenes. The mol ratio of CbFs to xylenes in the extract was 1.0. The molar composition of the xylenes present in the feed, raffinate and extract are tabulated below:

The above test shows that a high purity metaxylene product, i. e., about 95% meta-xylene and a high purity para-xylene product can be obtained by the use of about 4 theoretical extraction stages.

The figure shows an illustrative embodiment of our process. This figure demonstrates the treatment of a narrow boiling fraction in the xyiene boiling range, i. e., 270 to 300 F. which has been derived from the hydroforming of a virgin naphtha. The aromatic hydrocarbon content of this feed stock is ethylbenzene, l2 mol percent; ortho-xylene, V21; meta-xylene, 48; and para-xylene, 19. The non-aromatic hydrocarbons of this feed amount to 55 volume percent of the total feed. The process described in this preferred embodiment of our process removes all the xylenes from the feed and converts much of the ethylbenzene into benzene and meta-diethylbenzene in a rst step, and in a second step separates the xylenes into separate high purity isomeric fractions. In this example 1 high purity means in excess of 95 mol percent of the yparticular isomer.

In the first step of this process we show a tower-type of continuous countercurrent operation for the removal of substantially all the xylenes from the mixed feed. This tower can be packed with HF-resistant materials, such as, Raschig rings, Berl saddles, alumina balls, etc. Although we show a tower operation, we are not limited to the use of a tower and can use a series of batch countercurrent extraction zones. The separation factor for the removal of xylenes from non-complexible hydrocarbons is so great that in many cases a satisfactory degree of extraction can be obtained by a single stage contaeting, i. e., only a single contacter and a settler are needed in the extraction zone. We prefer to use at least two stages when removing substantially all the xylenes from a feed stock of this type.

The mixed feed from source II is passed by way of line I2 into about the vertical midpoint of extraction tower I4. The exact point of feed entry will vary somewhat with the feed and the conditions of operation, e. g., in some cases the point of feed entry can be near the bottom of the tower. The complex formation is exothermic and to permit the maintenance of a substantially constant temperature in tower Id, heat exchangers IS, Ii and I8 are placed therein. These heat exchangers permit operation in the range of 30 to 80 F. throughout the tower. The tower may be operated with a temperature gradient from bottom to top, in some types of operation.

Substantially anhydrous liquid HF from source 2l is passed through line 22 into vessel 23, which vessel 23 is provided with agitating means not shown. Finely divided CbFs from storage 28 is passed by way of line 21 into vessel 2li. Many methods are known for introducing a finely divided solid into a line and conveying the material into a closed vessel, e. g., storage 26 may be equipped with a star valve at the exit thereof and line 27 may be equipped with conveying iiights for moving the solid. In Vessel 23, the liquid HF and the CbF5 form a slurry-when, as is usually the case, more CbF5 is used than is soluble in the liquid HF--which slurry is passed through line 2S into an upper part of tower I4. In this illustration the CbF5 is added to the tower along with the liquid HF. However, the CbFs could be added along with the feed or could be injected into the tower directly; the treating agent may be added to the tower at one point as shown here, or at several points along the height of the tower between the point of feed entry and the top of the tower. Another method of introducing the CbFs into the system is to add CbCl5 into vessel 23 Where the chloride reacts wi-th to produce CbF5. Additional liquid HF must be added to vessel 23 to participate in the reaction and leave the desired amount of liquid HF for use in the extraction zone. When adding CbCls, means for venting HC1 should be provided on vessel 23.

In this illustration we use 200 volume percent of liquid HF based on the mixed feed and 1.3 mols of CbFs per mol of xylenes present in the mixed feed and 0.6 mol of CbFf, per mol of ethylbenzene present in the mixed feed. We have found that a slight excess of CbF5 over the theoretical requirement is necessary in order to obtain substantially complete removal of xylenes from a mixed feed. However, we. keep the excess addition as low as possible in order to reduce the amount of solid Cbl:` present in the extractor, and subsequently in the extract phase. This is done in order to reduce side reactions or" extractor i4 are also applicable to the operation of extractor H3.

In order to obtain a degree of separation such that will produce high purity' meta-xylene and para-xylene, the amount of CbF5 present should be at least about 1 mol per mol of meta-xylene present in the feed from line |H. The amount of liquid HF usedv in extractor H3 is about 300 volume percent based on xylenes in the feed. The temperature of contacting in extractor H3 is maintained uniformly Yat '70 F. for a contacting time of about 15 minutes; pressure in tower H3 is about 15 p. s. i. g. We prefer to operate on a mixture of xylenes and inert hydrocarbons. We attain this condition in extractor H3 by introducing pentane from source |3| and line 32 at a point near the bottom of extractor H3. The amount of pentane added is about 100 volurne percent based on xylenes charged to the tower from line H3. By introducing the pen-tane into the tower in this way, we obtain the desired dilution of the xylene feed and also obtain the advantages of good phase separation.

Liquid HF from line |22 is passed through valved line |34 into the top of tower H3 in order to wash out some of the entrained CbF5 in the ranate phase. The rainate phase and entrained HF and CbF5 is passed out of extractor H3 through line |36 into coalescer |31. The recovered HF and CbFs is returned to the extractor from the bottom of the coalescer through line |38. The ramnate phase from coalescer |31 is passed through line 14|, heater |42 and line |43 into stripper |44, which stripper is provided with internal heater |46.

Stripper idd is operated to remove overhead the HF and pentane present in the rainate'phase. rThe HF and pentane vapors pass overhead through line |43, are condensed in cooler |5| and pass through line |52 into separator |53. Liquid HF from separator |53 is withdrawn by line |513 and is recycled by lines not shown to line |22, for reuse in the process. Pentane is withdrawn from separator |53 byline 56 and is recycled to line |32 by lines not shown for reuse l in the process. A high purity para-xylene product is withdrawn from stripper |44 by way of line |58 and is sent to storage not shown.

The extract phase consisting of liquid HF, complex and pentane is withdrawn from extractor i S3 through line it; and is passed through heater |52 and line |55 into decomposer |64. Decomposer 84 is provided with an internal heater |66. Decoinposer es may be operated at temperatures somewhat above the boiling point of liquid HF in order to reduce the size of vessel. Appreciableisomerization of the meta-xylene to an equilibrium mixture of xylene isomers takes place at temperatures much in excess of about 125 F., so we prefer to operate deconiposer |54 at temperatures below about :3" HF vapors are" taken overhead through line 58, are condensed' in cooler i6?? and are passed to valved line IT The bottoms in de'composer |64 consist of solid, finely divided CbFt precipitate and high purity meta-xylene. rIh-ese bottoms are withdrawn through valved line iid and are passed into filter ii. Filter iii-3 is similar in construction and operation to hli'er The meta-xylene-product passes out of the filter by way of valved line VZ?. T ned in. filter 'F51 is re'- rnoved by baclwashing with liquid- HF from` line i? i. The slurry of HF and CbF5 from lter |75 is passed through valved line lg'int'o vessel |"3` for reuse in the process.

In order to improve the efficiency of operation in extractor i3, a reflux of meta-xylene is introduced near the bottom of the extractor. This reux may be obtained from line l'l and is introduced into the extractor by way of valved line itl. When operating with a redux, it is necessary to add an additional amount of CbFs into the tower over that needed to complex the metaxylene present in the feed. We add l mol of CbFs to extractor i3 for each mol of meta-xylene lntroduced into the extractor by way of line I8 i.

The product meta-xylene is sent to storage by way or" line |85. rhe product 4Ineta-xylene contains about mol percent of meta-xylene, between about 0.5 and 1% of pentane, and the remainder para-xylene. When it is desired to have a substantially pure aromatic hydrocarbon product, this pentane impurity can be removed by a simple distillation.

We do not wish to be bound by the above ernbodiment as the only Way of carrying out our process. Many other variations are possible and We include these within the scope of the invention. For example, instead o decomposing the extract phase from extractor the extract phase may be introduced into a second extractor and sufficient meta-xyiene in the presence of a suitable amount of diluent hydrocarbon introduced into the second extractor to spring the ortho and para-xylenes rom their complex. Other methods of recovering the Cbt from the decomposed extract phase can used, such as, decantation followed by recycle of a thick slurry of CbF5 and aromatic hydrocarbons. Oi' course additional CbF is needed in this method of operation in order to rec-ever the recycled aromatic hydrocarbons.

We claim:

1. A process for treating a mixture of isomeric lower dialkyl-benzenes, which process comprises contacting said mixture at a temperature below about F. with an amount of liquid HF sufficient to form a separate acid phase, and an amount o CbF5 whichV is not sufficient to cause all or said isomeric lower diakylbenzenes to pass into said acid phase, and separating a raffinate phase from said acid phase and wherein the relative ratio of isomeric lower dialkylbenzenes in said acid phase is different from the relative ratio in said raiiinate phase and the ratios in both of said phases are different from the ratio in said mixture.

2. The process of claim l wherein the amount of CbFs is less than about l mol per mol of diallrylbenzene present in said` mixture and the amount of liquid HF is between about 5 and 500 volume percent based on said mixture.

3.A The process of' claim l -wherein the alkyl substituents of said lower dialkylbenzenes contain between l and 5 carbon atoms.

Li. A process for separating a mixture of at least two xylene isomers, which process comprises contacting said mixture at a temperature between about 0 and 125 F., with between about 5 and 505 volume percent of liquid HF based on said mixture and CbF5 in an amount less than about l mol per mol of xylenes in said mixture, separating a rairinate phase from an extract which extract phase comprises lit-uid HF, .CbFs and xylenes and wherein the ratio between the xyl'en'e isomers in. said extract phase is different Vfrom the ratio in saidl raffinate phase and the ratios in said extract phase and said ranate phase are different from the ratio in said mixture. 5. Theprocess of claim` 4 whereiny said' mixture comprises essentially meta-xylene and paraxylene.

A process for separating meta-xylene from admixture with a least one other xylene isomer, which process comprises contacting said mixture at a temperature below about 90 F. with between about 100 and 300 volume percent, based on said mixture, of liquid l-IF and between about 0.3 and 1.5 mois of CbFs per mol of meta-xylene in said mixture, separating a rainate phase from an extract phase wherein said raffinate phase has a molal ratio of meta-xylene to the other xylene isomers therein lower than the ratio in said mixture, and wherein the molal ratio of meta-xylene to other xylenes in said extract phase is higher than the ratio in said mixture, and recovering xylene isomers from said extract phase.

7, The process of claim (i wherein said contacting is carried out in a, continuous countercurrent apparatus and wherein the amount or" CbFs is about 1 mol per mol of meta-xylene in said mixture and wherein the mixture of xylene isomers in Said extract phase contains about 95% metaxylene.

8. A process for recovering xylenes from a mixture of Ca aromatic hydrocarbons, which process comprises contacting said mixture at a temperature below about 90 F. with between about 5 and 50o volume percent of liquid HF based on said mixture, and between about 0.3 and 1.5 mols of CbFs per mol of xylene in said mixture, and about 0.5 mol of CbFs per mol of ethylbenzene in said mixture and recovering xylene isomers from the products of said contacting.

9. The process of separating a mixture of xylene isomers, which process comprises contacting said mixture at a temperature below about 125 F., in the presence of an inert hydrocarbon diluent, with between about 5 and 500 volume percent of liquid HF based on xylenes and less than about 1 mol of CbFs per mol of xylenes, separating a raflinate phase, comprising essentially said diluent and xylenes, from an extract phase, comprising essentially liquid HF, xylenes, CbFs and a minor amount of said diluent, and wherein the relative ratio of the xylenes in said extract phase is different from the relative ratio of xylenes in said rafnate phase, and wherein both of said ratios are different from the ratio of xylenes in said mixture of xylene isomers, and recovering the xylenes from said extract phase and from said raffinate phase.

10. The process of claim 9 where in said inert hydrocarbon diluent is present in an amount between about 50 and 200 volume percent based on said Xylene.

11. The process of claim 9 wherein said inert hydrocarbon diluent is selected from the group 1S consisting of parafnic hydrocarbons containing between 3 and 6 carbon atoms.

12. A process of recovering meta-xylene from admixture with at least one other xylene isomer and ethylbenzene, which process comprises contacting said mixture at a temperature below about F., in the presence of an inert hydrocarbon diluent, with between about and 300 volume percent of liquid HF based on Ca aromatic hydrocarbons and CbFs in an amount of about 1 mol per mol of meta-xylene in said mixture, and about 0.5 mois per mol of ethylbenzene in said mixture, separating a railnate phase comprising essentially inert hydrocarbon diluent. benzene and C3 aromatic hydrocarbons from an extract phase comprising essentially liquid HF, CbFs, xylenes and C10 aromatic hydrocarbons and recovering from said extract phase a mixture of xylene isomers consisting predominantly of metaxylene.

13. A process for renng a hydrocarbon oil containing polyalkylbensenes, which process comprises contacting said oil at a temperature below about 200 F. with from about 0.1 and 100 weight percent of CbFs in the presence of from about 10 to 500 volume percent of liquid HF, both based on said oil, and separating a raffinate phase from an extract phase.

14. The process of claim 13 wherein the usage of CbFs is between about 0.1 and 25 weight percent.

l5. The process of claim 13 wherein the usage of liquid HF is between about 30 and 300 volume percent.

16. The process of claim 13 wherein said temperature is between about 50 and 100 F.

1'7. A process for removing polyalkylbenzenes from a naphtha which contains substantially no other extractable materials, which process comprises contacting said naphtha with about 1 mol of CbF5 per mol of polyalkylbenzene to be removed in the presence of about 10 to 500 volume percent, based on said naphtha, of liquid HF at a temperature below about 100 F., and separating a raffinate phase from an extract phase, which extract phase contains extracted pclyalkylbenzenes.

References Cited in the le of this patent UNITED STATES PATENTS Name Date Lien et al. Nov. 7, 1950 OTHER REFERENCES Number 

1. A PROCESS FOR TREATING A MIXTURE OF ISOMERIC LOWER DIALKYL-BENZENES, WHICH PROCESS COMPRISES CONTACTING SAID MIXTURE AT A TEMPERATURE BELOW ABOUT 125* C. WITH AN AMOUNT OF LIQUID HF SUFFICIENT TO FORM A SEPARATE ACID PHASE, AND AN AMOUNT OF CBF5 WHICH IS NOT SUFFICIENT TO CAUSE ALL OF SAID ISOMERIC LOWER DIALKYLBENZENES TO PASS INTO SAID ACID PHASE, AND SEPARATING A RAFFINATE PHASE FROM SAID ACID PHASE AND WHEREIN THE RELATIVE RATIO OF ISOMERIC LOWER DIALKYLBENZENES IN SAID ACID PHASE IS DIFFERENT FROM THE RELATIE RATIO IN SAID RAFFINATE PHASE AND THE RATIOS IN BOTH OF SAID PHASES ARE DIFFERENT FROM THE RATIO IN SAID MIXTTURE. 